fossil

Fossil Coral

Hexagonaria (agatized coral)

Mohs hardness of 6.5 to 7; brown, gray, and white coloration; vitreous to waxy luster; hexagonal crystal structure of quartz replacement.

Identified October 24, 2026More fossil →

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Physical properties

Mohs hardness of 6.5 to 7; brown, gray, and white coloration; vitreous to waxy luster; hexagonal crystal structure of quartz replacement.

Formed through permineralization where silica-rich groundwater replaces ancient coral skeleton calcium carbonate over millions of years.

Used primarily in lapidary arts, cabochons, decorative carvings, and collected as a unique fossil specimen.

Also known as Petoskey stone when found in specific northern regions; the pattern reveals ancient rugose coral calices.

Identified by distinct star-like or honeycomb patterns on cut surfaces; common in sedimentary limestone formations worldwide.

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image